Vtol boundary layer control system



Dec. 19, 1961 J. F. KLAPPROTH VTOL BOUNDARY LAYER CONTROL SYSTEM FiledMarch 11, 1960 m m M ,qrragusy- United States Patent Office PatentedDec. 19, 1961 3,013,744 VTOL BOUNDARY LAYER CONTROL SYSTEM John F.Klapproth, Cincinnati, Ohio, assignor to General Electric (Jompany, acorporation of New York Filed Mar. 11, 1960, Ser. No. 14,243 8 Claims.(Cl. 244-12) The present invention relates to a VTOL or verticaltake-off and landing system and more particularly, to such a systemwherein the lift per horsepower for a given fan size is considerablyincreased.

In VTOL systems, which are considered to be aircraft capable oftaking-off and landing vertically, many variations have been proposed.One of the common systems is the use of large fans in the fuselage orwings which are designed to move large quantities of low velocity airtherethrough in order to obtain upward lift on the vehicle body on whichthe fans are mounted. In such a system, it is apparent that limitationsare encountered on the size of the fan that can be used. Thus, it isdesirable to increase the effectiveness of a given wing or fuselagemounted fan by some suitable means in order to obtain the necessary liftwithin the confines of the structure available. In other Words, it isdesirable to obtain more lift per horsepower with restriction to a givenfan diameter which may be required by certain installations. As ageneral rule in such applications, to increase the effectiveness perhorsepower, it is necessary to use a larger diameter fan, more massflow, and a lower pressure ratio across the fan. This effectiveness perhorsepower to fan diameter is normally in a one to one relationship.Where structural limitations are encountered, it is desirable to removethis one to one relationship to give some degree of flexibility andselection in the fan and still obtain a certain lift per horsepower.

It is a primary object of the present invention to disclose a VTOLsystem enabling more effective use of the available fan forming part ofthe system.

Another object is to disclose and provide such a system wherein a givendiameter fan and a given horsepower may be utilized more effectively.

A further object is to provide such a system wherein flexibility isprovided in the selection of the fan diameter to provide the same liftwhere there is no limit on the fan diameter.

Briefly stated, my invention provides a body such as a wing or fuselagehaving a duct for the passage of air to provide lift on the body, andhaving fan means disposed in the duct to force the air therethrough andprovide the lift. A diffusing boundary layer control means is provideddownstream of thefan to controllably spread the fan discharge along thelower surface of the body and produce a fiow area larger than thecross-sectional area of the duct.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which I regard as myinvention, it is believed the invention will be better understood fromthe following description taken in connection with the accompanyingdrawing in which:

FIGURE 1 is a schematic diagram showing the invention applied to afuselage of an aircraft;

FIGURE 2 is a schematic showing of a modification of the inventionapplied to a body such as a wing;

FIGURE 3 is another modification similar to that shown in FIGURE 2;

FIGURE 4 is still another modification of the invention as it might beapplied to a wing; and

FIGURE 5 is a modification using a combination of FIGURE 2 and FIGURE 3and illustrating a means for controlling diffusion.

- 2 and 3 for illustration, to be described hereinafter.

Referring first to FIGURE 1, there is shown a VTOL system having a bodyto be lifted which may be any suitable aircraft 10. Disposed in the body10 such as'a fuselage, there is provided a duct 11 which preferablypasses from the top of the aircraft to the bottom thereof in asubstantially vertical directiontherethrough. In order to move largemasses of low velocity air through the duct and provide lift on the body10, suitable fan means 12 is provided in the duct. The fan 12 may bedriven by any suitable means not shown and, in all cases, may be placedrelative to the duct as in FIGURE 1 or in the duct substantially at theoutlet or exit plane as in FIG- URES 2, 3 and 5.

It is known in such an installation that in general the lift perhorsepower available from the fan 12 increases as the pressure ratioacross the fan is reduced. However, a reduced pressure ratio generallyresults in a reduced air flow through the fan 12, severely reducing thetotal lift available from a given fan diameter. As a consequence,conventional arrangements having the fan through-flow velocityessentially equal to the effective discharge velocity have a nearlyunique relation between lift per horsepower and lift per square foot offan area. Under these conditions, any attempt to increase the lift perhorsepower can only be realized at the expense of reduced lift for agiven fan size or an increase in fan size for a required lift.Conversely, attempts to reduce the size of the fan for a given lift canbe realized only at a sacrifice in lift per horsepower or an increase inrequired horsepower.

By the present invention it is possible to circumvent the nearly uniquerelation generally existing between lift per horsepower and lift persquare foot of fan area, to take advantage of reduced fan pressure ratiowithout the associated reduction in available lift or to increase faneffectiveness without the associated penalty in lift per horsepower.

This is accomplished first in FIGURE 1 by providing a diffuser boundarylayer control means downstream of the fan 12. Effective boundary layercontrol permits a spreading or diffusion of the flow along the undersurface of the body. Such diffusing through boundary layer control maytake a number of forms as shown in FIGURES Referring again to FIGURE 1any suitable manifold means 15 may be provided to effect the boundarylayer control and diffuse the flow downstream of the fan and provide thearea increase. In effect, the instant invention then widens out thedischarge area of the fan from that shown at area 13 to that shown atthe effective area 14. By this means, any given diameter fan may beselected to have an effective lift per horsepower equivalent to that ofa much larger diameter fan and thus be utilized in more confined areaswhere structural limitations are imposed. To say it another way, as thevelocity downstream of the fan is decreased by means of diffusingthrough boundary layer control, the lift per horsepower is increased.Any suitable means to obtain this result is contemplated by theinvention herein disclosed.

Referring next to FIGURE 2, a specific structure is shown forillustration by which the diffusing by boundary layer control downstreamof the fan may be obtained. It will be noted in this figure that thebody 10 may be thought of as the wing as opposed to the fuselage inFIGURE 1 since the invention is applicable to either. The diffusion isobtained in this modification by the provision of ducts 16 connectingthe upstream and the downstream portions of the fluid passage. Byproviding the ducts 16 leading as shown in FIGURE 2, it is possible touse the upstream portion of the fluid passage or duct through the body10 as a low pressure sink to remove the boundary layer fluid adjacentthe exit plane of the main flow duct through the bleed ducts in thedirection shown by the arrows. It will be apparent that this is a formof boundary layer control to form a diffuser by means of which thedownstream air flow may be induced to follow the lower surface of thewall of body 10 and thus widen out the discharge area into an arealarger than that of the duct.

A further modification is shown in FIGURE 3 of a typical diffusingmechanism that may be used to controllably spread the fan discharge overthe lower surface of the body into an area larger than the duct. In FIG-URE 3, the body 10 may again be illustrative of a wing having a fan 12therein driven by any suitable means to induce air flow from the uppersurface to the lower. Where the previous FIGURE 2 bled boundary layerair from the lower surface in order to induce the flow to follow thesurface of body 10, the instant modification has pipes or equivalent 17that contain high pressure fluid, such as air, to be discharged throughslots 18 peripherally of the fan in a direction tangential to the bodysurface near the exit plane of the duct to induce the flow to follow thelower surface of body 10 as shown in FIGURE 3. Thus, this form ofblowing boundary layer control also controllably spreads the fandischarge along the lower surface to produce a flow area larger thanthat of the duct.

Referring to FIGURE 4, a mechanical means of doing the same spreadingaction is illustrated. This modification employs difiuser vanes 19 thatphysically bend the flow of fluid downstream of the fan to controllablyspread it into a larger area than the duct area as shown. Obviously,this latter modification entails some losses by providing physicalstructure in the passage whereas the modifications of FIGURES 2 and 3may be controlled by suitable valve means not shown and do not imposeany physical obstructions in the fluid flow since both modifications inFIGURES 2 and 3 are out of the main flow and disposed along theperiphery of the fan.

In order to obtain a unique relation between net lift from the systemfor each operating condition, a positive means of controlling the amountof diffusion is desirable. Such control means may, in a winginstallation, fix the downstream diffusion border or separation point bythe usual wing flap as shown at 20 in FIGURE 5. A positive location ofthe stagnation streamline can be obtained on the upstream side by acontrolled extendable or rotatable portion of the wing as flap 21 whichmay be extended as shown in FIGURE in dotted lines during lift orretracted as shown in solid lines during cruise or high speed flight andused in intermediate positions during transition. FIGURE 5 alsoillustrates a combination of diffusing by boundary layer control meanssuch as ducts 16 of FIGURE 2 and pipe 17 of FIGURE 3, either or both ofwhich may be used to obtain the desired flow pattern.

It will be apparent that in those applications where a restriction isapplied on the available diameter of fan that can be used, the instantinvention permits more effective lift per horsepower by providing aneffective diffuser downstream of the fan by means of boundary layercontrol to controllably spread the fan discharge along the lower surfaceof the body and produce a flow area larger than the duct.

While I have hereinbefore described a preferred form of my invention,obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

I claim:

1. A VTOL system including a body having a duct therethrough, fan meansdisposed in the duct to direct air through the duct and create a liftforce on the body, and boundary layer control diffusing means downstreamof the fan to controllably spread the fan discharge along the lowersurface of the body and produce a flow area larger than the duct.

2. A VTOL system including a body having a substantially vertical ducttherethrough, fan means disposed in the duct to direct air through theduct and create a lift force on the body, and boundary layer controldiffusing means adjacent the exit plane of the duct to controllablyspread the fan discharge along the lower surface of the body and producea flow area larger than the duct.

3. A VTOL system including a body having a substantially vertical ducttherethrough, fan means disposed in the duct to direct air downwardthrough the duct and create a lift force on the body, and boundary layercontrol diffusing means in the body adjacent the fan periphery tocontrollably spread the fan discharge along the lower surface of thebody and produce a flow area larger than the duct.

4. Apparatus as described in claim 3 wherein the boundary layer controldiffusing means includes slot means connecting the duct on each side ofthe fan whereby downstream boundary layer air is bled to the ductupstream of the fan.

5. Apparatus as described in claim 3 wherein the boundary layer controldiffusing means includes slot means in the body directing high pressureair jets along the lower body surface to induce the fan discharge tospread along the lower surface of the body and produce a flow areadownstream of the fan larger than the duct.

6. A VTOL system including a body having a substantially vertical ducttherethrough, fan means disposed in the duct substantially in the planeof the lower exit of the duct to direct air downward through the ductand create a lift force on the body, and boundary layer controldiffusing means adjacent the fan periphery on the downstream side tocontrollably spread the fan discharge along the lower surface of thebody and produce a flow area larger than the duct cross-sectional area.

7. Apparatus as described in claim 6 wherein the body is a wing of anaircraft.

8. Apparatus as described in claim 6 wherein the body is a fuselage ofan aircraft.

References Cited in the file of this patent UNITED STATES PATENTS

